Overpopulation is a troublesomemeasurement in a human society. In an animal grouping, it's quite easy to define; it's the point at which the available resources (including space/privacy) are overwhelmed by the demands of the group, and as a result, some members die off until the group (population) is back below its supportable level.

In humans, however, the situation is never that clear-cut. For one thing, we've developed - ta-da! - transportation, which means that we can (theoretically) either a) leave the area or b) truck resources in. So who's to say when 'overpopulation' comes in? It's almost impossible to use this term without providing a context or a criteria with which to measure it. For example, you might say that New York City is overpopulated for the number of access points into Manhattan. Or, you might say that Mexico City is overpopulated because it cannot transport in enough resources to support its population (not true yet, as far as I know).

These days, the term is usually used to describe an entire ecosystem, and in our case, the only one we got - the Earth (mom Gaia) herself. Some environmentalists, human rights advocates, and other types claim that the Earth is overpopulated or is heading inexorably in that direction. However, there is evidence to the contrary; in some nations, notably European ones which enjoy relative internal security and calm polities, it has been observed that economic pressures have given rise to a 'flattening out' of the population growth curve. Germany, for example, at one point in early 1990s when her economy was flat, achieved ZPG or 'Zero Population Growth.' The hypothesis to explain this was that as people became unable to viably support more children, the average family size shrank to the point required to sustain the population level and no more.

So as humans, perhaps we can remain in harmony wth our 'environment' - it's just that our environment is a bit more subjective than that of the beasts and birds.

It is pretty obvious that if every two people have exactly two children, the population will not grow. Two people have two children, then die. Their children have two children, then die. Those children have two children, and then die themselves.

Unfortunately, it is not a simple matter to ensure that every couple has only two children. Many of the countries in the world have very high population growth -- the average couple produces significantly more than two children. This is why overpopulation is such a huge threat.

Suppose that, rather than two children, each couple produces eight. This is a fairly extreme scenario, but serves to demonstrate:

In four generations, perhaps 60 or 70 years, the population has increased 50-fold. Okay, this is bad. We need to stop it. So, we develop a horrible nerve gas that tends to render the target sterile and deploy it all over the place. It's not pretty, but better than the alternative. We've effectively reduced the population growth to ZPG: every couple has two children.

The parents don't die as soon as their children are born. They stick around for a while. Lets say they remain alive for two generations for the sake of this demonstration. This means that, while the fourth generation is just getting ready to make babies, the second generation is getting ready to rest in peace. But they're still consuming resources. Not only the 128 people in the fourth generation must be supported, but the 40 people in the two previous generations.

Even if the fifth generation only consists of 128 people (because of all that nerve gas), the population has STILL grown: 8 people have died off, but been replaced with 128 new people. It's better than the 512 people they would have been replaced with before the gas, but it's still a net growth of 120 people... and the next generation will increase the total by 88 before the population finally stabilizes.

"Yay!", we exclaim. It might have been tough, but we've finally stabilized the population. While food may be a bit tight divided among 384 people, it's much better than the 2688 people we would have had without attending to the population growth problem.

In short, overpopulation is as huge a problem as it seems. It has an obvious solution: make everyone stop having so many kids. However, implementing that solution (at least, in a humane manner) is very difficult, and the longer we take to implement it, the longer and harder the adjustment to an eventual stable population growth will be. We can’t just get on the TV and say “Hey, everyone, stop having kids!”, because the people having the most kids don’t have TV’s. They probably don’t have toothbrushes or flush toilets, either, and they definatley don’t have condoms. And, to my knowledge, we don’t have any surefire sterility-causing nerve gas. Our methods are generally more along the lines of education about birth control, and are at a very local level, not a global one.

And hamster bong, you're absolutely correct that the earth can support more people if they each use a smaller quantity of resources. However, it can not support continued exponential growth, no matter how environmentally conscious people are. (And the countries with the highest population growth tend to be third-world, where recycling your empty beer cans isn’t usually an issue).

It seems that, in technologically ascendant nations such as the United States, population growth is actually slowing over time. In Italy in particular, zero population growth has already been reached, and it currently experiences fewer births than deaths. The growth still continues to skyrocket in less affluent nations, and I would presume in less affluent portions of the rich nations (there are certainly inner-city areas where the average family size is much greater than national), but as the world's population gets (in general, and very slowly in some areas, due to various processes too complex to get into here) richer, it would mean that the overall population growth would slow as well, eventually stabilizing at zero population growth, at around the seven-to-twelve-billion people range according to the information I received in class.

Reasons for this include people generally having better access to methods of birth control in more affluent nations, being more familiar with the dangers and responsibilities of having large families, infant mortality rates are now lower so couples feel less compelled to have many children so that at least a small number will reach adulthood, there are plain out fewer couples since more never marry, with pressures of career and other concerns weighing more heavily on them, and, importantly, and don't laugh, they are more likely to have better things to do that to produce offspring.

China, with its unique combination of low per-capita income and enormous population, has passed laws, to some success, to try to curb its growth. But throughout much of the industrialized world (and now, I suppose, the "informationalized" world), birthrates have fallen to below China's current, state-mandated limits.

As a result, world population growth rates are starting to decline, and in fact a contrary problem has arisen: with the demographic spreads of many nations tending to become elderly-heavy, how can the younger generations hope to support them?

Searching the web for information to substantiate this odd class-learnt fact, I found: http://www.worldbank.org/depweb/english/modules/social/pgr/
http://www.uic.edu/classes/osci/osci590/15_3%20Population%20Growth%20II.htm

I think there are two essential questions involved here:
1)Whether overpopulation is seriously such a huge problem.
2)If it is not, why is such a big fuss made about it.

Firstly I feel that overpopulation is not a very major problem. Malthus theory of population growing in geometric progression and food growing in arithemetic progression has been experimentally proven wrong for centuries now. The reasons are very simple, and anyone who is familiar with Voltaire'sprey-predator equations knows them. I wouldnt like to go into them here but the basic idea is that there is a time delay factor involved. Anyway, whatever the mathematics I would like to emphasize that we have not seen geometric growth of population and arithemtic growth of food . Food production has kept up with the population. So the first thing that is required is the rejection of the Malthus theory.

The second thing that is required is to realise that the essential problem here is the equitable distribution of resources. One one scale this is a problem within a country. A few people are very rich, and hog resources and this is what creates a shortage.

On a second more serious scale this is a world-wide problem. The first world is worried about the population of the third world but it is the first world which controls the majority of the world's resources. Thus here again you have a situation where a very very small portion of the world controls a huge portion of the available resources. I feel that the least the first world can do under the circumstances is to avoid talking about population problems in the third world.

A final point I wish to make here is this. If we must speak of population, what we must speak of is population density not population in absolute terms. The population density of Europe is higher than that of India. So I dont see the justification of pressurizing India to control its population.

Finally let me briefly summarize my arguments:
1)I said that that the Malthusian theory has been proven experimentally wrong, so the resource problem is not as serious as it is made out to be.
2)If there is an apparent shortage of resources it is because of a non-equitable distribution and not because of any inherent shortage in resources.
3)Finally The first world controls most of the world's resources and the population density in Europe is one of the highest in the world.Therefore it is absolutely unjustifiable for the first world to talk about population problems.

I think all this brings up a question with sinister implications. If population is not such a serious problem why is such a big deal made of it. The answer seems to be clear. Since the primary problem is one of non-equitable resource distribution, people/countries who control a disproportional share are insecure. "It is essential to ask the poor to control their population because if they dont they will soon begin to ask for their rights"- and what would the rich do then?

A brief reply to hramyaegr's article below. If you plot thedata given below the first thing to notice is that population growth picked up around 1800. It would be naive to base a law of geometric growth of population on this data because there was a clear sociological factor that caused high population growth in the 19th and 20th century-The Industrial Revolution. Industrial capitalism requires a large amount of labour and this is what leads to large population growth. It is ironical that it is the capitalists who later get worried about overpopulation.
Secondly there is this small point about non-equitable distribution of resources which hramyaegr seems to have completely overlooked.
Finally as rfc1394 points out high population growth in the Third World is often a result of low life expectancy. So equitable distribution of resources would be an immediate cure for the population problem.

"Since evolving about 200,000 years ago, our species has proliferated and spread over the Earth. Beginning in 1650, the slow population increases of our species exponentially increased. New technologies for hunting and farming have enabled this expansion. It took 1800 years to reach a total population of 1 billion, but only 130 years to reach 2 billion, and a mere 45 years to reach 4 billion."

"Transgressing the carrying capacity for one period lowers the carrying capacity thereafter, perhaps starting a downward spiral toward zero. David Klein's classic study of the reindeer on St. Matthew Island illustrates the point.26 In 1944 a population of 29 animals was moved to the island, without the corrective feedback (negative feedback) of such predators as wolves and human hunters. In 19 years the population swelled to 6,000 and then "crashed" in 3 years to a total of 41 females and one male, all in miserable condition. Klein estimates that the primeval carrying capacity of the island was about 5 deer per square kilometer. At the population peak there were 18 per square kilometer. After the crash there were only 0.126 animals per square kilometer and even this was probably too many once the island was largely denuded of lichens. Recovery of lichens under zero population conditions takes decades; with a continuing resident population of reindeer it may never occur. Transgressing the carrying capacity of St. Matthew Island reduced its carrying capacity by at least 97.5 percent. It is facts like these -- repeated over and over again in game management experience -- that justify the ecolate game manager in viewing carrying capacity as partaking of the sacred. I do not think it is going too far to assert and defend the sanctity of the carry capacity."

Garrett Hardin, An Ecolate View of the Human Predicament, http://www.dieoff.org/page80.htm, with more information available at http://www.ishmael.org/Education/Science/carry_capacity.shtml

Exponential growth has also been demonstrated in just about every 10th grade biology class in the last twenty years, by using a small dish, and a tiny sample of yeast. Not that yeast is alone in this--many of those same classrooms likely did the same with fruit fly populations. Even viruses have exponential growth patterns (http://www.scidiv.bcc.ctc.edu/rkr/Biology201/lectures/Virus.html); a rare disease will slowly increase in occurrence until its growth explodes.

As shown, geometric growth can and does occur, and as in the case of the reindeer on St. Matthew Island, geometric growth of a population can and does occur when the growth pattern of the food is not geometric; the result of geometric growth is that the population will strip its environment of its natural resources until the environment is no longer able to maintain that population. The carrying capacity of that population will then have been reduced, and a dieoff will occur. Geometric growth does occur, and it has its consequences.

Population density is not the only factor in determining whether or not overpopulation is a problem. Though India has a lower population density and is currently somewhat able to sustain its population, it has a much higher growth rate than that of Europe. As stated above, Italy and Germany both have or have very nearly zero population growth. India has the highest level of population growth of any country and within ten years will surpass China as the most populated country in the world. To say that it is unjustifiable for a world population to talk about world population problems is ridiculous. Overpopulation is a serious problem, and it does affect everyone, as the cumulative effects of six billion people affect all six billion people.

Regarding fitting the population of the world into Texas:

"If you divided the world's 6 billion humans into Texas's 261,914 square miles, each person could claim .028 acres of land. It is obvious, however, that the land in Texas, (or even the land in North America for that matter), would not be able to sustain these people. Resource experts say a minimum of 0.17 acres of arable land is needed to sustain a person on a largely vegetarian diet without the intense use of fertilizers and pest controls.

An estimated 253 million people currently live in countries with scarce arable land --which have on average no more than 0.17 acres available per person -- and this population is expected to at least triple by 2025 if current trends continue. Only 11 percent of the Earth consists of arable land, and that area is rapidly diminishing due to erosion, salinization and a decline in the practice of fallowing land."

http://www.zpg.org/Reports_Publications/Reports/report83.html

In addition:

"If just the present world population of 5.8 billion people were to live at current North American ecological standards (say 4.5 ha/person), a reasonable first approximation of the total productive land requirement would be 26 billion ha (assuming present technology). However, there are only just over 13 billion ha of land on Earth, of which only 8.8 billion are ecologically productive cropland, pasture, or forest (1.5 ha/person). In short, we would need an additional two planet Earths to accommodate the increased ecological load of people alive today. If the population were to stabilize at between 10 and 11 billion sometime in the next century, five additional Earths would be needed, all else being equal -- and this just to maintain the present rate of ecological decline (Rees & Wackernagel, 1994).

"While this may seem to be an astonishing result, empirical evidence suggests that five phantom planets is, in fact, a considerable underestimate (keep in mind that our footprint estimates are conservative). Global and regional-scale ecological change in the form of atmospheric change, ozone depletion, soil loss, ground water depletion, deforestation, fisheries collapse, loss of biodiversity, etc., is accelerating. This is direct evidence that aggregate consumption exceeds natural income in certain critical categories and that the carrying capacity of this one Earth is being steadily eroded. We should remember Liebigs "Law of the Minimum" in this context. The productivity and ultimately the survival of any complex system dependent on numerous essential inputs or sinks is limited by that single variable in least supply. In short, the ecological footprint of the present world population/ economy already exceeds the total productive area (or ecological space) available on Earth."

In poor and "Third World" countries, most people are involved in some form of (usually subsistence) farming or some equivalent of living off the land. As a result, one has children - and lots of them - because life is hard and many of them will die. But some of them will survive to farm and then they can support their parents when they are unable to work.

In wealthy countries, most people are involved in some non-farmoccupation where children are not necessary as a potentially productive asset. Which means that in wealthy countries people have fewer children because they are not necessary for future support - we have the ability to purchase pensions and life insurance to support ourselves or our families if we die - and thus children represent a consumption item like leasing a Mercedes Benz.

Also, the development of better access to medical care, labor saving developments like machines and electricity, as well as new drugs has increased lifespans everywhere as well as caused death rates to plummet.

As a result of this, what is happening is that the rich countries are either reaching or even exceeding ZPG (because we're not just having Zero Population Growth, we are actually losing population) and the poor countries are breeding even faster. In fact, over the last 30 years, it is my understanding that all of the gains in population in the United States has been either through immigration or children of recent immigrants. (Once someone has been here a while they also don't need to have a large family for the same reason as everyone else: we're not heavily dependent upon farming so large families are unnecessary).

Further, most of the problems of food are not due to high levels of population - in fact, in many places there are tremendous surpluses of food - but because of politics and mismanagement of resources. Many years ago, Dr. Thomas Sowell, a nationally syndicated columnist pointed out that you could fit the entire world's population - all 6+ billion people - into single-family homes at a lower density than most American cities in a space no larger than the size of the State of Texas. (If you include the amount of space necessary to include cropland, then it would require a space the size of the State of Alaska.)

Besides providing for you in your old age, children have economic
effects here and now. In a subsistence economy, a child is an asset
very early in its life- even a four or five year old can look after
chickens. Subsistence agriculture requires a lot of labor, and the
cheapest, easiest way to get it is to grow it. There's a clear, short
term economic incentive to have more children.

Compare to the developed economy. In our world, a child is a
liability, not an asset. Children do not work, but they still eat. They
demand video games and designer clothing. Then you send them to college.
When it's all over, maybe they'll support you in your old age, but our
customs aren't nearly as strong in that respect. Your kids might just put
you in a nursing home and forget about you. This is why developed
countries often experience ZPG.

The really key question about population growth, then: Will the birth
rates fall fast enough to give us ZPG before population grows beyond
sustainable levels? This in turn hinges on how quickly the Third World
develops, which is a complicated question for another node. At any rate
we seem to have some time, since we can easily grow enough food to
support a considerable increase, if we could manage to distribute the
food to those who need it.

As Azure Monk points out, every increase in longevity will destabilize
this again. The question here is whether agricultural technology will
keep pace with medical technology. If it doesn't, there will be
problems. In the extreme, science fiction case, that of true immortality,
we would of course require a zerobirth rate in order to have
ZPG.